CN107462097B

CN107462097B - Variable-aperture capillary core applied to loop heat pipe system and processing method thereof

Info

Publication number: CN107462097B
Application number: CN201710863813.7A
Authority: CN
Inventors: 汪冬冬; 王金新; 包向军; 陈�光; 楚化强
Original assignee: Anhui University of Technology AHUT
Current assignee: Anhui University of Technology AHUT
Priority date: 2017-09-22
Filing date: 2017-09-22
Publication date: 2022-07-05
Anticipated expiration: 2037-09-22
Also published as: CN107462097A

Abstract

The invention discloses a pore diameter-variable capillary wick applied to a loop heat pipe system and a processing method thereof, belonging to the field of phase change heat transfer and flow of porous media. According to the capillary core, powder particles with a higher melting point and fibers with a lower melting point are selected to be mixed and sintered, the temperature is controlled to enable the fibers to be completely sintered to form a capillary core framework, the powder particles are not sintered, and the pore diameter can be automatically adjusted according to the movement of a thermal load in the space of the fiber framework; the capillary core is applied to a loop heat pipe, the aperture of powder particles is automatically adjusted under different heat loads, the suction force of the capillary core is adjusted, a phase change interface is prevented from penetrating into the capillary core, the heat transfer resistance of the capillary core during working is reduced, and meanwhile, the flow resistance can be reduced, so that the running performance of the loop heat pipe is improved.

Description

Variable-aperture capillary core applied to loop heat pipe system and processing method thereof

Technical Field

The invention relates to the technical field of porous medium phase change and flow, in particular to a pore diameter variable capillary core applied to a loop heat pipe system and a processing method thereof, and can also be applied to the fields of aviation thermal control, electronic equipment cooling and the like.

Background

A Loop Heat Pipe (LHP) is a high-efficiency passive heat transfer device for transferring heat by utilizing phase change of a working medium, and has the advantages of strong heat transfer capacity, low heat transfer resistance, long transmission distance, no moving part and the like. The loop heat pipe is a separated heat pipe which is composed of an evaporator, a compensation cavity, a steam pipeline, a liquid pipeline and a condenser, and the working process of the loop heat pipe is as shown in the attached figure 1: after the evaporator 6 is heated by being attached to the heating surface of the heat dissipation component, heat is conducted into the capillary core 11 through the wall surface of the evaporator 6, the capillary core 11 absorbs the heat, working media close to the heating surface are subjected to phase change, steam enters the condenser 8 through the steam pipeline 7 and is condensed into liquid, the condensed liquid working media are subjected to capillary suction force of the capillary core 11 in the evaporator 6 and flow back to the compensation cavity 10 through the liquid pipeline 9, the liquid in the compensation cavity 10 supplements the liquid in the capillary core 11 to be evaporated, and the heat of the heat dissipation component is continuously transferred to the outside through the evaporation-condensation cycle.

The capillary core in the loop heat pipe has a large heat exchange area due to the porous structure, when the loop heat pipe runs, the working medium in the capillary core is subjected to phase change, and simultaneously, the capillary core is also the only power source of the whole loop heat pipe system due to the capillary suction force of the micropores, so that the capillary core is called as the heart part of the loop heat pipe. The capillary wick used at present usually adopts sintered metal capillary wick, and the common capillary wick is sintered capillary wick of single powder. On the basis, some pore-forming agents are usually added into the existing capillary core to form a double-pore-diameter capillary core, the suction force of the capillary core is increased by using small pores, the internal flow resistance is reduced by using large pores, and the generated steam is favorably separated. But these advantages disappear when the capillary wick pore former is added to a certain percentage.

Atoms on the surfaces of all particles of the metal powder contact surface are migrated in the sintering process of the metal powder, so that a sintering neck is formed, and the bonding of the contact parts among all metal powder particles is strengthened; meanwhile, the positions of the metal powders are relatively fixed, and under the condition of large heat load, the phase change interface gradually extends into the capillary core, the thickness of a steam layer is increased, and the thermal resistance of the capillary core is increased; when the loop heat pipe works, the heat loads are different, the phase interface is unstable, the temperature fluctuation is large, and the overall operation performance is poor. Therefore, the design of a high-performance capillary core with a multi-aperture structure, low flow resistance, low evaporation thermal resistance and capability of stabilizing an evaporation interface is a problem which needs to be solved urgently in the industry at present.

Through retrieval, the Chinese patent application number: 2016102861131, filing date: in 2016, 4, 28 days, the invention and creation name is: the application discloses a powder-microfiber composite porous capillary wick applied to a loop heat pipe system, the capillary core is formed by mixing and sintering metal powder and microfibers, the metal powder is connected through the microfibers, a small-aperture porous medium structure formed by the microfibers among the powder and a large-aperture porous medium structure formed by the particle powder are realized, the unique structure of the capillary core endows the capillary core with the flowing heat transfer characteristics of high capillary suction force, low flow resistance, high surface evaporation rate and low effective heat conductivity, and the capillary core is applied to a loop heat pipe system, the heat transfer and mass transfer in the loop can be enhanced, the evaporation phase change interface of the working medium is stabilized, the heat leakage to the compensation cavity is reduced, and the temperature fluctuation of the system operation is eliminated or weakened, so that the operation performance of the loop heat pipe is improved.

Also as in chinese patent application No.: 2011103986112, filing date: in 2011, 12 and 5 days, the invention and creation name is as follows: the application discloses a preparation method of a porous capillary wick with controllable pore diameter, which is characterized in that soluble salt powder which does not react with matrix powder is uniformly mixed into the matrix powder of a sintering raw material of the capillary wick, and the mixed powder is cold-pressed and molded into a shape required by the capillary wick; pressureless sintering or pressure sintering is carried out on the molded raw materials under the protection of inert gas, and then water is used for washing out soluble salts to obtain the catalyst. The application has the advantages of simple preparation process and low cost, and the capillary core with high strength and controllable porosity is manufactured.

In summary, in the prior art, a great deal of disclosures are made on the structure design and the manufacturing method of the capillary wick, but the requirements of the industry on practice are still difficult to meet, and the continuous research on the capillary wick is a pursuit of the industry with no focus.

Disclosure of Invention

1. Technical problem to be solved by the invention

The invention aims to overcome the defects of different thermal loads and poorer running performance of a loop heat pipe in the prior art, and provides a variable-aperture capillary wick applied to a loop heat pipe system and a processing method thereof.

2. Technical scheme

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

the invention relates to a pore diameter variable capillary core applied to a loop heat pipe system, which comprises fibers and powder particles, wherein the fibers are used as an internal framework to fix the powder particles in the capillary core, the capillary core also comprises fiber pores, powder pores and powder fiber pores, and the powder particles can move in the framework under the meniscus pressure difference caused by the change of thermal load so as to adjust the pore diameter of the capillary core.

Further, the powder porosity varies with the movement of the powder particles.

Furthermore, the fiber is a low melting point metal fiber, and the melting point is 1000-1200 ℃.

Further, the aspect ratio of the fiber is 5 to 100.

Furthermore, the powder particles are high-melting-point metal powder particles, and the melting point is 1500-1800 ℃.

The invention relates to a processing method of a pore diameter variable capillary core applied to a loop heat pipe system, which is characterized in that fibers, powder particles and a filler are mixed and sintered, the sintering temperature is 40-50% of the melting point of the fibers, the completely sintered fibers are distributed around the powder particles to form a capillary core framework, the unsintered powder particles can move in the framework, and the powder particles are correspondingly balanced at different positions according to different heat loads borne by the capillary core.

Further, the filler is Na₂CO₃Or NaCl or urea.

Further, the aspect ratio of the fiber is 5 to 100.

3. Advantageous effects

Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:

(1) according to the pore diameter variable capillary core applied to the loop heat pipe system, powder particles with higher melting points and fibers with lower melting points are mixed and sintered together, the powder particles can move in a framework according to meniscus pressure difference caused by heat load change and are correspondingly balanced in different pore diameters and positions, the requirement of suction force is met quickly, the flow resistance is reduced, the heat transfer characteristic of the system is optimized, the evaporation interface is stabilized, the evaporation thermal resistance is reduced, and therefore the operation performance of the whole system is improved.

(2) The pore diameter variable capillary core applied to the loop heat pipe system has the sintering temperature of 40-50% of the melting point of the fiber, so that the fiber is sintered to completely form a framework, the powder particles do not reach the sintering effect and cannot be bonded with other powder particles or fibers, and when the capillary core is subjected to different heat loads, the unsintered powder particles in the capillary core are correspondingly balanced in different pore diameters and positions, so that the pore diameter of the capillary core is automatically adjusted.

(3) The variable-aperture capillary wick applied to the loop heat pipe system can adjust the suction performance when the loop heat pipe works, and when the heat load is small, the suction performance is small, and the gaps among powder particles freely dispersed in the capillary wick can meet the requirement of the suction performance; when the heat load is larger, the powder particles are pushed by steam to be gathered, the pore diameter between the powders is reduced, and the suction property is increased, so that the phase change interface is stabilized, and the powder particles are prevented from penetrating into the capillary core.

(4) According to the pore diameter variable capillary core applied to the loop heat pipe system, the powder particles can move under the influence of the heat load and the phase change interface, the pore diameter among the powder particles can be changed, the automatic adjustment does not need any auxiliary work, and the application is very convenient.

(5) According to the variable-aperture capillary core applied to the loop heat pipe system, the powder particles are stabilized in the capillary core by virtue of the fiber framework, the sintering contact area between the powder particles and the fibers is low, and the heat conductivity coefficient is low; the contact between the unsintered powder particles and the fibers is limited in the capillary wick, and the powder particles are not completely in direct contact with each other, but the heat is transferred to the fibers and then transferred to the next group of powder particles, so that the effective heat conductivity coefficient of the capillary wick is greatly reduced, and the back heat leakage of the capillary wick is reduced.

(6) According to the pore diameter-variable capillary wick applied to the loop heat pipe system, the powder particles strengthen steam heating in the moving process, the circulating power of the loop heat pipe can be improved, and meanwhile, heat is rapidly transferred to the phase change interface to enhance heat transfer.

Drawings

FIG. 1 is a schematic view of a loop heat pipe in an operating state;

fig. 2 is a schematic structural diagram of a variable aperture wick applied to a loop heat pipe system according to the present invention;

fig. 3 is a schematic view of the capillary wick operating condition of the present invention under low thermal load;

fig. 4 is a schematic view of the working state of the capillary wick under normal thermal load;

fig. 5 is a schematic view of the operating state of the capillary wick of the present invention under high thermal load.

The reference numerals in the schematic drawings illustrate: 1. fibers; 2. powder particles; 3. fiber porosity; 4. powder porosity; 5. powder fiber porosity; 6. an evaporator; 7. a steam line; 8. a condenser; 9. a liquid line; 10. a compensation chamber; 11. a capillary core; 12. a liquid phase; 13. a phase change interface; 14. a gas phase; 15. phase change interface powder; 16. vapor layer powder.

Detailed Description

For a further understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

The present invention will be further described with reference to the following examples.

Example 1

As shown in fig. 2, the variable pore diameter capillary wick applied to the loop heat pipe system of the embodiment includes a fiber 1 and a powder particle 2, and further includes a fiber pore 3, a variable powder pore 4 and a powder fiber pore 5, where the fiber 1 serves as an internal skeleton to fix the powder particle 2 inside the capillary wick, the powder particle 2 can move in the skeleton under a meniscus pressure difference caused by a change in thermal load, and the powder pore 4 also changes along with the movement of the powder particle 2, so as to adjust the pore diameter of the capillary wick, and quickly meet the requirement of stabilization of a phase change interface 13 in the capillary wick, and the movement of the powder pore 4 can change the suction property according to the thermal load and optimize heat transfer.

In the embodiment, the capillary core is prepared by adopting metal raw materials with large melting point difference, wherein the fiber 1 is a low-melting-point metal fiber, the melting point is 1200 ℃, the length-diameter ratio is 5-100, the powder particle 2 is a high-melting-point metal powder particle, the melting point is 1800 ℃, and the proportion and the size of the powder particle 2 and the fiber 1 can be adjusted according to physical parameters required by the capillary core in practice, and are not described in detail herein.

The capillary core of the embodiment is processed by the following method: the fiber 1, the powder particles 2 and the filler are mixed and sintered at a sintering temperature of 40 to 50 percent of the melting point of the fiber 1, namely, a temperature suitable for sintering the fiber 1, wherein the filler is Na₂CO₃The pore diameter and the porosity of the capillary core can be optimally controlled. During sintering, when the fiber 1 is heated to about 0.4 times the melting point, many atoms of the powder particles 2 diffuse to form initial metal bonds between the particles, and when the heating is continued, atoms on the surfaces of the particles at the contact surfaces of the powder particles 2 migrate to form sintering necks, so that the contact parts of the powder particles 2 are bonded and strengthened. After the capillary core is completely sintered, the internal pore channels of the capillary core are reduced, so that the porosity of the capillary core is reduced, the capillary force is reduced, the suction capacity of the capillary core is reduced, and the circulating power of the capillary core is reduced in a loop heat pipe system. The incompletely sintered capillary core can ensure that the capillary core has higher surface heat transfer coefficient due to the unsintered powder particles 2, but has lower overall heat conductivity, so that the capillary core can ensure surface evaporation and reduce back heat leakage; meanwhile, on the distribution of the internal pore diameter, most pore channels of the powder particles 2 which are not completely sintered are reserved for the circulation of working media, so that the contact area is reduced, and the heat conductivity coefficient is reduced.

In this embodiment, the powder particles 2 with a higher melting point and the fibers 1 with a lower melting point are used, the fibers 1 are sintered completely to form a skeleton according to the difference of the melting points, the powder particles 2 do not reach the sintering effect and cannot be bonded with other powder particles 2 or fibers 1, and when the thermal load of the capillary core is different, the unsintered powder particles 2 inside are correspondingly balanced in different pore sizes and positions. Specifically, if 316L stainless steel powder and copper fiber are adopted, at the sintering temperature of 500 ℃, the copper fiber is completely sintered, while the stainless steel powder is not sintered and keeps the original shape, the copper fiber constructs the whole capillary wick framework, and the stainless steel powder moves inside the capillary wick framework.

In the embodiment, when the loop heat pipe works, heat is loaded to the capillary core, the working medium is heated to change phase, a gas-liquid interface is formed inside the capillary core, a phase change interface 13 is formed between the liquid phase 12 and the gas phase 14, the position of the powder particles 2 inside the capillary core changes along with the difference of heat load, as shown in fig. 3, the capillary core rapidly changes phase under low load to take away heat, and the phase change interface 13 is arranged at the bottom of the capillary core; as shown in fig. 4, as the thermal load increases, under normal thermal load, the phase change interface 13 moves upward, and the movement of the phase change interface powder 15 changes to reduce the pore size, increase the suction ability, and prevent the phase change interface 13 from going deep; as shown in fig. 5, the heat load continues to increase, and under a high heat load, the phase change interface 13 moves upward, the phase change interface powder 15 moves to change the pore size to reduce the pore size, so that the suction performance is increased, the phase change interface 13 is prevented from being greatly penetrated, meanwhile, the vapor layer powder 16 reciprocates under the action of vapor pressure, so that the heat transfer between the evaporator 6 and the phase change interface 13 is enhanced, and meanwhile, the effective heat conductivity coefficient of the capillary core is low, the back-to-back heat leakage is reduced, and the operating temperature of the whole system is reduced.

When the capillary core is actually used, the phase change interface 13 can be effectively regulated and controlled, the capillary core is prevented from entering the inside of the capillary core, the traditional capillary core phase change interface can enter the capillary core along with the increase of heat load, the capillary core with the variable aperture can adjust the suction performance when a loop heat pipe works, when the heat load is small, the suction performance is small, and the gap between the freely dispersed powder particles 2 in the capillary core can meet the requirement of the suction performance; when the heat load is larger, the powder particles 2 are pushed by steam to gather, the pore diameter between the powders is reduced, the suction performance is increased, and the phase change interface 13 is stabilized to prevent the powder particles from penetrating into the capillary core.

Secondly, the capillary core of this embodiment can automatically adjust the suction, reduces the flow resistance, and specifically, in the capillary core of this embodiment with variable aperture, unsintered powder particle 2 moves in sintered fiber 1 skeleton, and the pore space occupied by powder particle 2 is bigger, and working medium will always tend to flow into the channel with small resistance when flowing into the capillary core, and after being forced, powder particle 2 will move to the position with the smallest resistance to reduce the flow resistance, for the working medium circulation. When the loop heat pipe works, the powder particles 2 move under the influence of the heat load and the phase change interface 13, the pore diameter among the powder particles 2 is changed, when the pore diameter is increased, the suction force of the capillary core is reduced, and when the pore diameter is reduced, the suction force of the capillary core is increased.

Thirdly, the capillary core of the embodiment can reduce the effective heat conductivity coefficient and reduce heat leakage, specifically, the powder particles 2 are stabilized in the capillary core by the fiber 1 framework, the sintering contact area between the powder particles 2 and the fiber 1 is low, and the heat conductivity coefficient is low; the contact between the unsintered powder particles 2 and the fiber 1 in the capillary wick is limited, and the powder particles 2 are not completely in direct contact with each other, but the heat is transferred to the fiber 1 and then transferred to the next group of powder particles 2, so that the effective heat conductivity of the capillary wick is greatly reduced, and the back leakage heat of the capillary wick is reduced.

It should be noted that, in this embodiment, the movement of the powder particles 2 can also enhance heat transfer, when the loop heat pipe works, when a thermal load is large, the phase change inside the capillary wick occurs fast, and more steam is generated, when steam enters the steam pipeline 7 through the capillary wick, the movable powder particles 2 located below the phase change interface 13 will rapidly and repeatedly move in the framework under the action of steam pressure, and the powder particles 2 enhance the heating of the steam in the moving process, improve the circulating power of the loop heat pipe, and simultaneously rapidly transfer heat to the phase change interface 13 to enhance heat transfer.

It should be further noted that the capillary wick of this embodiment can also effectively reduce the operating temperature of the loop heat pipe, and specifically, the variable aperture capillary wick has a lower thermal conductivity and less back-to-back heat leakage, so that the temperature of the working medium in the compensation cavity 10 is lower, and meanwhile, according to the difference in thermal load, the aperture of the powder particles 2 is changed, the suction force of the capillary wick is adjusted, the phase change interface 13 and the evaporation rate are stabilized, the thermal resistance of the vapor layer is reduced, and the operating temperature of the entire loop heat pipe is reduced.

When the loop heat pipe operates, the pore diameter of the capillary core with the variable pore diameter can be changed according to different heat loads, the moving position of the internal powder particles can meet the requirement of suction force quickly, the flow resistance is reduced, the heat transfer characteristic of the system is optimized, the evaporation interface is stabilized, the evaporation thermal resistance is reduced, and therefore the operation performance of the whole system is improved.

Example 2

The difference between the variable-aperture capillary wick applied to the loop heat pipe system of the embodiment and the embodiment 1 is that the fiber 1 is a low-melting-point metal fiber, the melting point is 1000 ℃, the powder particles 2 are high-melting-point metal powder particles, and the melting point is 1500 ℃; the filler in the mixing and sintering is urea.

Example 3

The difference between the variable-aperture capillary wick applied to the loop heat pipe system of the embodiment and the embodiment 1 is that the fiber 1 is a low-melting-point metal fiber, the melting point is 1100 ℃, the powder particles 2 are high-melting-point metal powder particles, and the melting point is 1600 ℃; the filler used in the mixing and sintering process is NaCl.

The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.

Claims

1. The utility model provides a be applied to variable aperture capillary core of loop heat pipe system which characterized in that: the capillary core comprises fibers (1) and powder particles (2), wherein the fibers (1) are used as an internal framework to fix the powder particles (2) in the capillary core, the capillary core also comprises fiber pores (3), powder pores (4) and powder fiber pores (5), and the powder particles (2) can move in the framework according to a meniscus pressure difference caused by heat load change so as to adjust the pore size of the capillary core; the powder pores (4) change with the movement of the powder particles (2); the fiber (1) is a low-melting-point metal fiber, and the melting point is 1000-1200 ℃.

2. The variable aperture wick applied to a loop heat pipe system according to claim 1, wherein: the aspect ratio of the fiber (1) is 5-100.

3. The variable aperture capillary wick applied to a loop heat pipe system of claim 1, wherein: the powder particles (2) are high-melting-point metal powder particles, and the melting point is 1500-1800 ℃.

4. A processing method of a pore diameter variable capillary core applied to a loop heat pipe system is characterized by comprising the following steps: the fiber (1), the powder particles (2) and the filler are mixed and sintered, the sintering temperature is 40% -50% of the melting point of the fiber (1), the completely sintered fiber (1) is distributed around the powder particles (2) to form a capillary core framework, the unsintered powder particles (2) can move inside the framework, and the powder particles (2) are correspondingly balanced at different positions according to different heat loads on the capillary core.

5. The method for processing the variable aperture capillary wick applied to the loop heat pipe system according to claim 4, wherein: the filler is Na₂CO₃Or NaCl or urea.

6. The method for processing the capillary wick with the variable aperture applied to the loop heat pipe system as claimed in claim 4, wherein: the fiber (1) is a low-melting-point metal fiber, and the melting point is 1000-1200 ℃.

7. The method for processing the capillary wick with the variable aperture applied to the loop heat pipe system as claimed in claim 6, wherein: the aspect ratio of the fiber (1) is 5-100.

8. The method for processing the capillary wick with the variable aperture applied to the loop heat pipe system as claimed in claim 6, wherein: the powder particles (2) are high-melting-point metal powder particles, and the melting point is 1500-1800 ℃.